The present invention relates to modules adapted to be placed in side-by side relation in the surf to define an off-shore reef-like barrier which protects beaches against erosion and causes deposition of sand and pebbles to restore and build up the shoreline. This device is an improvement over our earlier module disclosed in U.S. Pat. No. 4,367,978 and the prior art referred to therein.
While the module of our prior patent proved to be effective in dissipating the energy of the incoming surf and in causing the deposition of waterborne sand, certain aspects of its design tended to cause scouring of sand from the bottom beneath and immediately adjacent to the module. First, there is a natural tendency for barriers in the water to rotate seaward (i.e., the top of the barrier tends to tilt toward the sea) because part of the energy of the incoming surf is deflected downward and scours away the supporting sand beneath the seaward edge of the barrier. Secondly, the central opening in the bottom of our previously patented module, which was intended to aid in anchoring the module to the sea bottom, tended to cause further scouring of sand from beneath the module.
Thirdly, the flap-like valve member of our previously patented module tended to cause too much back pressure on the module from the return flow of water toward the sea. This pressure increased the tendency of the module to rotate seaward and also could cause sufficient forces to push a module out of alignment with its neighboring modules. By excessively reducing the available flow path for returning water through the module, such flow was diverted into the spacing between adjacent modules. The increased velocity through these restricted spaces caused additional scouring of the sand from both the shoreward and seaward sides of the module.
All of these phenomena described above tended to cause misalignment of the row of modules or to cause the modules to sink too deeply into the bottom, thereby decreasing their effectiveness.
While modules having a generally similar shape to those described in our prior patent have been made without the central bottom opening, the planar uninterrupted bottom of such modules was unable to adequately anchor the module to the sea bottom.
Accordingly, it is the primary object of the present invention to provide an improved module which effectively dissipates the energy of the surf, causes deposition of sand to restore or build up the shoreline, and also minimizes the tendency of the energy of the moving water to scour sand from beneath and around the module. Furthermore, it is an object of the present invention to provide means for effectively anchoring or stabilizing the position of the module on the sea bottom, without causing it to sink excessively into the sea bottom.